Radio frequency current transformer



Dec. 22, 1953 R. M. BAKER E RADIO FREQUENCY CURRENT TRANSFORMER Filed Oct. 18, 1950 INVENTOR Robert M. Bdker. BY

WITNESSES: 5%

Patented Dec. 22, 1953 UNITED STATES PATENT OFFICE RADIO FREQUENCY e'uiuiiiur TRANSFORMER Robert M. Baker, Catonsville, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, l?a., a corporation of Pennsylvania Application October 18, 1950, serial No. 190,743

7 Claims.

This invention relates to current transformers and particularly to current transformers suit able for use at radio frequencies.

Radio-frequency current transformers having a helically wound copper tube primary winding that may be utilized for cooling purposes and a single-turn secondary have been employed heretofore in the electrical industry. iow'e'ver, one of the problems in manufacturing such a radio-frequency current transformer has been to obtain sufii'cient insulation betweenthe primary and secondary winding so as to withstand the high radio-frequency voltages present.

An object of this invention is the provision of primary and secondary windings for radio-frequency current transformers which are so insulated from each other that they function properly when subjected to the radio-frequency voltages impressed on such transformers.

Another object of this invention is the utilization of an inorganic refractory tubing having conductive coatings on the inside as the primary Winding of a current trans-former suitable for radio frequencies, the refractory material utiliz'ed in the primary winding serving as insulation between the windings.

Other objects of the invention will appear from reading the specification and claims in connection with the accompanying drawing, in which:

Figure 1 is a view in section taken along the line II of Figure 2 of the radio-frequency current transformer embodying the features of this invention, and

Figure 2 is a plan view of the radio-frequency current transformer embodying the features of this invention.

Referring to the drawing, the modification of a radio-frequency current transformer shown generally at in embodies the features of this invention, As illustrated, the radio-frequency current transformer Ill comprises a primary Winding I2 formed from an inorganic refractorytube 14 and on which coatings of conducting material have been applied over the inner surface of the tube [4, which will be described in detail hereinafter. A single-turn secondary winding it having terminals I! and ll surrounds and conforms to the circular configuration of the primary winding l2, and an insulating material [8 is disposed between the primary winding I2 and the secondary winding l6, which insulating material l8 will be described hereinafter in detail.

In production, the tube 14 g of the primary winding I2 is formed from an inorganic refractory material, such as zircon porcelain, electrical porcelain, steatite, orthe like, in a plastic unfired state. The first step in forming the primary winding I2 is to extrude the plastic inorganic refractory material into a long hollow tube l4, which in this embodiment is of rectangular cross section and has a bore 19 for the passage of a cooling fluid. The tube l4 having been extruded, the inner surfaces at the two endsof the tube H are then fashioned to facilitate the attachment of a metal water fitting 20 having a passage 2| in continuation of bore 19. The fitting 20 also constitutes a. portion of a terminal for connecting the transformer Ill to a power source (not shown). The tube 14 while still in its plastic state is Wound into a helical coil with the adjacent turns touching. It is then dried and fired in the conventional manner.

In order to improve the mechanical and physical properties, particularly the strength and surface smoothness of the ceramic tube I 4, both its inner and outer surfaces are glazed in any Well-known manner. Two metallic coatings 22 and 24 of electrical conducting material are then applied to the inner surface of the tube M.

The metallic coating 22 is applied by chemically depositing a layer or film of platinum,

' sold, or silver on the inner surface of the tube 14. This metallic coating 22 facilitates the bond ing of additional metal to the inner surface of the ceramic tube [4. As. shown, the coating 22 extends over the entire inner surface of the tube I4 so as to cover that portion of the surface to which water fittings 20 are attached and makes electrical contact with the fittings 2t. A satisfactory method of producing and applying the coating 22 of platinum to a ceramic, such as porcelain, so as. to enable the bonding of a metal to porcelain is described in Patent No. 1,852,093. Y

Once the platinum has been chemically deposited on the inner surfacev of the tube 14, the second coating 24 of copper or silver is electrically deposited on the first coating 22. In practice, it has been found satisfactory to electrically deposit the copper or silver until a coating 0.005 inch thick is obtained.

In order to electrically deposit the copper or silveron the fist coating 22, a copper or silver wire (not shown), which acts as a plating anode, is threaded through the bore 49. The first coating 22 is utilized as the plating cathode. Glass beads. (not shown) are threaded onto the wire anode: at intervals, thus acting as an insulator between the plating anode and the first coating 22. When the plating anode has been properly positioned in the spiral passage, plating solution (not shown) isv then continuously pumped through the bore i9. Passing an electrical current between the plating cathode and anode results, inthe electrical depositing of the coating 24 of either copper or silver on the first coating 22. depending on whether a copper or silver electrolyte'is used. The plating process having been completed, the wire anode is removed from the tube M and the pumping of the plating solution is discontinued. The coatings 22 and 24 having been applied, the metal water fittings 20 are attached in any suitable manner, as by brazing or soldering, to the ends of the tube Hi. When the transformer 10 is in use,

the coatings 22 and 24 serve as an electrical conductor.

In order to cool the primary winding i2 when the transformer 10 is in service, water is continuously pumped through the bore it, the water being obtained from any suitable source (not shown). The procelain tube l4 serves as a support for the applied coatings 22 and 2d and also functions as an insulator between the conducting metallic coatings 22 and 2d and the secondary winding Hi. This added insulation is necessary in order for the transformer 10 to withstand for a suiiicient length of time the high radio-frequency voltages present in radio-frequcncy current transformers.

The secondary winding [6 is superimposed on and conforms to the configuration of the pri mary winding 12. For the purpose of cooling, a tube 26 is either brazed or welded to the secondary winding I6. It is to be understood, however, that other cooling means than that shown could be used for cooling the secondary winding it.

In order to provide additional insulation, a layer 18 of insulating material is so applied as to surround the outer surface of the primary winding 52 and conform to its configuration. This layer it of insulating material may be a resilient, low-loss, resinous composition. EX- apmles of suitable insulating material for this purpose are polyethylene of a molecular weightv of 10,000 to 40,000 and higher, polyisobutylene of a molecular weight of up to 150,000 and higher, interpolymers and mixtures of polyethylene and isobutylene, organopolysiloxanes and particularly elastomeric dimethylsiloxanes, polytetrafluoroethylene, polytrifluorochloroethylene, ethyl cellulose, polyvinyl carbazole, polystyrene, chlorinated rubber, and silicone-rubber as described in Patents 2,472,629 and 2,480,620.

The radio-frequency current transformer l shown and described herein has many advantages over other such transformers. As hereinbefore mentioned, the radio-frequency current transformer embodying the teachings of this invention stands up under the high radio-frequency voltages impressed on the transformer, and as a result, the life of the transformer is long.

[he tube id is formed from a porcelain coil, such as zircon porcelain, electrical porcelain, steatite or the like, and can usually be obtained as a stock item from most suppliers, which is an important factor when it is necessary to repair the transformer on short notice. And except for the plating operation, the construction and assembly of the radio-frequency current transformer i0 embodying the teachings of this invention is simple and straight-forward since the workmen do not require special training in applying insulations.

I claim as my invention:

1. In a transformer, in combination, a primary winding comprising an inorganic refractory tubing, a coating of conducting material chemically deposited over the inner surface of the inorganic refractory tubing so as to obtain a continuous adherent contact, a coating of conducting material electrically deposited on the said chemically deposited conducting material, and a secondary winding inductively associated with the primary winding.

2. In a transformer, in combination, a primary winding comprising an inorganic refractory tubing, a continuous coating of conducting material chimically deposited over the inner surface of the inorganic refractory tubing so as to obtain a continuous adherent contact, a coating of conducting material about 0.065 inch thick electrically deposited on the said chemically deposited coating, and a secondary winding inductively associated with the primary winding.

3. In a transformer, in combination, a primary winding comprising an inorganic refractory tubing, a coating of platinum glaze chemically deposited over the inner surface of the inorganic refractory tubing so as to obtain a continuous adherent contact and another coating comprising a conducting material electrically deposited on the coating of platinum glaze, and a secondary winding inductively associated with the primary winding.

4. In a transformer, in combination, a primary winding comprising an inorganic refractory tubing, a coating of silver chemically deposited over the inner surface of the tubing so as to obtain a continuous adherent contact and another coating comprising a conducting material electrically deposited on the silver coating, and a secondary winding inductively associated with the primary winding.

5. In a transformer, in combination, a primary winding comprising an inorganic refractory tubing wound into a helical coil, a coating of platinum glaze chemically deposited over the inner surface of the tubing so as to obtain a continuous adherent contact and a coating of copper electrically deposited on the coating of platinum glaze, and a secondary winding superimposed on the primary winding and being inductively associated therewith.

6. In a transformer, in combination, a cooled primary winding comprising an inorganic refractory tubing, a coating of platinum glaze chemically deposited over the inner surface of the inorganic refractory tubing so as to obtain a continuous adherent contact and a coating of silver electrically deposited on the coating of platinum glaze, and a cooled secondary winding superimposed on-the primary winding and inductively associated therewith.

7. In a transformer, in combination, a watercooled primary Winding comprising an inorganic refractory tubing wound into a helical coil, a coating of platinum glaze chemically deposited over the inner surface of the tubing so as to obtain a continuous adherent contact and a coating of copper electrically deposited on the coating of platinum glaze, and a single-turn, water-cooled secondary winding superimposed on the water-cooled primary winding and inductively associated therewith.

ROBERT M. BAKER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,273,135 Ohnesorge et a1. Feb. 17, 1942 2,366,290 Rudd Jan. 2, 1945 FOREIGN PATENTS Number Country Date 498,116 Great Britain Jan. 3, 1939 

